Project Summary Venous thromboembolism (VTE) is an important cause of morbidity and mortality in patients with cancer. Approximately 20% of patients with cancer develop, and 10% die, from VTE. However, the risk of VTE in cancer is highly variable. Identifying high-risk patients is important to optimize benefit from thromboprophylaxis, but solitary risk factors have not proven to be useful VTE predictors. A clinical scoring system developed by one of the PIs of this application (?Khorana score?) combines five clinical variables to segregate patients into high, intermediate, or low risk groups, and is the most widely used system for predicting VTE in cancer. The risk of VTE in the low-risk group is < 1%, however only 18% of patients in the high-risk group develop VTE; thus, the positive predictive value is low. Moreover, most patients fall into an intermediate-risk group for which improved risk prediction is needed. Several hemostatic biomarkers, including circulating tissue factor (TF), D-dimer, and P-selectin have been assessed for their ability to predict VTE, but found to have limited utility. New and innovative biomarkers are therefore urgently needed. In this application, we propose a two-phase study to define novel biomarkers of cancer-associated VTE. We first propose a discovery phase to identify novel candidate biomarkers. This encompasses Aim 1, which examines biomarkers of contact and complement activation, and Aim 2, which examines circulating plasma/exosome microRNA profiles. Emerging data has linked the contact activation system (CAS), which consists of FXII, prekallikrein and kininogen and leads to activation of FXI and the intrinsic coagulation pathway, to pathologic thrombosis; however, the role of the CAS in cancer-associated thrombosis (CAT) has not been studied. Our compelling preliminary data indicates the importance of this system, and we have developed an array of novel assays of CAS activity. In Aim 1, we will prospectively assess the predictive value of these assays in three large cohorts of patients with pancreas, lung, and colorectal cancers. Complement is also activated by the CAS, is linked to thrombosis in hematologic disorders, and our preliminary studies demonstrate that C3a and C5a are associated with outcomes in pancreatic cancer; thus, we will further evaluate these biomarkers as well. In Aim 2, we will explore another emerging area of biomarker research- circulating microRNA (miRNA). We hypothesize that plasma from cancer patients at greatest risk of VTE contains increased levels of specific miRNAs, or unique miRNA profiles, and our preliminary studies have identified six plasma miRNAs associated with VTE in cancer. In the second, validation phase of our proposal, Aim 3 will validate candidate biomarkers discovered in Aims 1 and 2 using plasma samples from an independent 700 patient cohort of cancer patients obtained from 3 large, multinational studies. We will incorporate this data into a new VTE prediction model using risk modeling strategies. Our proposed studies are highly responsive to RFA HL-18-021, and will lead to novel biomarkers and improved risk stratification strategies to predict and prevent VTE in cancer.